Corneal and lenticular biometry in Chinese children with myopia

Myopia prevalence and ocular biometry in children and adolescents at different altitudes: a cross-sectional study in Chongqing and Tibet, China

OBJECTIVE

To investigate the differences in myopia prevalence and ocular biometry in children and adolescents in Chongqing and Tibet, China.

DESIGN

Cross-sectional study.

SETTING

The study included children and adolescents aged 6-18 years in Chongqing, a low-altitude region, and in Qamdo, a high-altitude region of Tibet.

PARTICIPANTS

A total of 448 participants in Qamdo, Tibet, and 748 participants in Chongqing were enrolled in this study.

METHODS

All participants underwent uncorrected visual acuity assessment, non-cycloplegic refraction, axial length (AL) measurement, intraocular pressure (IOP) measurement and corneal tomography. And the participants were grouped according to age (6-8, 9-11, 12-14 and 15-18 years group), and altitude of location (primary school students: group A (average altitude: 325 m), group B (average altitude: 2300 m), group C (average altitude: 3250 and 3170 m) and group D (average altitude: 3870 m)).

RESULTS

There was no statistical difference in mean age (12.09±3.15 vs 12.2±3.10, p=0.549) and sex distribution (males, 50.4% vs 47.6%, p=0.339) between the two groups. The Tibet group presented greater spherical equivalent (SE, -0.63 (-2.00, 0.13) vs -0.88 (-2.88, -0.13), p<0.001), shorter AL (23.45±1.02 vs 23.92±1.19, p<0.001), lower prevalence of myopia (39.7% vs 47.6%, p=0.008) and flatter mean curvature power of the cornea (Km, 43.06±1.4 vs 43.26±1.36, p=0.014) than the Chongqing group. Further analysis based on age subgroups revealed that the Tibet group had a lower prevalence of myopia and higher SE in the 12-14, and 15-18 years old groups, shorter AL in the 9-11, 12-14 and 15-18 years old groups, and lower AL to corneal radius of curvature ratio (AL/CR) in all age subgroups compared with the Chongqing group, while Km was similar between the two groups in each age subgroup. Simple linear regression analysis showed that SE decreased with age in both the Tibet and Chongqing groups, with the Tibet group exhibiting a slower rate of decrease (p<0.001). AL and AL/CR increased with age in both the Tibet and Chongqing groups, but the rate of increase was slower in the Tibet group (p<0.001 of both). Multiple linear regression analysis revealed that AL had the greatest effect on SE in both groups, followed by Km. In addition, the children and adolescents in Tibet presented thinner corneal thickness (CCT, p<0.001), smaller white to white distance (WTW, p<0.001), lower IOP (p<0.001) and deeper anterior chamber depth (ACD, p=0.015) than in Chongqing. Comparison of altitude subgroups showed that the prevalence of myopia (p=0.002), SE (p=0.031), AL (p=0.001) and AL/CR (p<0.001) of children at different altitudes was statistically different but the Km (p=0.189) were similar. The highest altitude, Tengchen County, exhibited the lowest prevalence of myopia and greatest SE among children, and the mean AL also decreased with increasing altitude.

CONCLUSIONS

Myopia prevalence in Tibet was comparable with that in Chongqing for students aged 6-8 and 9-11 years but was lower and myopia progressed more slowly for students aged 12-14 and 15-18 years than in Chongqing, and AL was the main contributor for this difference, which may be related to higher ultraviolet radiation exposure and lower IOP in children and adolescents at high altitude in Tibet. Differences in AL and AL/CR between Tibet and Chongqing children and adolescents manifested earlier than in SE, underscoring the importance of AL measurement in myopia screening.

Characteristics of myopic and hyperopic eyes in patients with antimetropia

CLINICAL RELEVANCE

Antimetropia is a rare type of anisometropia in which one eye is myopic and the fellow is hyperopic, This optical condition condition permits the evaluation of both sides of the emmetropisation process failure in the same individual by minimising genetic and environmental factors.

BACKGROUND

This study aimed to evaluate the ocular biometric, retinal, and choroidal characteristics of myopic and hyperopic eyes of antimetropic subjects older than six years.

METHODS

In this retrospective study, myopic and hyperopic eyes of 29 antimetropic patients with a spherical equivalent (SE) difference of at least 2.00D between the eyes were included. Axial length (AL), mean corneal keratometry, anterior chamber depth, the proportion of anterior chamber depth in AL, crystalline lens power, central macular thicknesses, disc-to-fovea distance, fovea-disc angle, peripapillary retinal nerve fibre layer (RNFL) thicknesses, and subfoveal choroidal features were compared between the eyes. The prevalence of amblyopia was determined. Refractive parameters and total astigmatic profile were evaluated in eyes with and without amblyopia.

RESULTS

The median absolute SE and AL differences between the eyes were 3.50D (interquartile range:1.75) and 1.18 mm (interquartile range:0.76), respectively (p < 0.001). Myopic eyes had lower crystalline lens power and proportion of anterior chamber depth in AL, and longer disc-to-fovea distance. Macular thicknesses, global RNFL, and temporal RNFL were thicker in myopic eyes, and there was no difference in other RNFL quadrants. Despite the increase in the choroidal vascularity index, other choroidal parameters were decreased in myopic eyes. Amblyopia was found in three of the myopic eyes and seven of the hyperopic eyes (p = 0.343). The highest interocular SE and AL difference and the highest frequency of anisoastigmatism were observed in patients with amblyopia in the myopic eye.

CONCLUSION

Each ocular structure may respond differently to, or may be affected differently by, ametropic conditions.

Effects on radius of curvature and refractive power of the cornea and crystalline lens by atropine 0.01% eye drops

PURPOSE

The morphological changes in the cornea and crystalline lens have not been closely evaluated after the administration of atropine 0.01%. This study aims to evaluate the radii of curvature and refractive power of the cornea and lens in myopic eyes during atropine 0.01% treatment.

METHODS

Children aged 6-14 years with myopia <-6.0 D were randomized to receive atropine 0.01% once nightly with single vision lenses or simply wear single vision lenses. Ocular biometric parameters were measured using the IOLMaster 700 biometry and the radii of corneal and lenticular curvature were simulated using a customized program.

RESULTS

At the 9-month visit, 69 atropine-treated eyes and 50 control eyes were included in the final analyses. In atropine-treated eyes, the posterior corneal surface steepened (-0.05 ± 0.13 mm) and the anterior lenticular surface flattened (0.20 ± 0.69 mm) significantly within 3-6 months, whereas the posterior corneal surface and anterior lenticular surface gradually flattened (0.07 ± 0.23 and 0.32 ± 0.80 mm respectively) in the control eyes over 9 months. The difference in the change of corneal refractive power was significant between groups (-0.03 ± 0.18 D vs. 0.11 ± 0.24 D, p = 0.001), while that in the change of lenticular refractive power was statistically insignificant (0.01 ± 0.92 D vs. -0.22 ± 0.86 D, p = 0.161).

CONCLUSIONS

The administration of atropine 0.01% exhibited a clinically short and subtle impact on the cornea and lens, which may shed light on new targets of action for atropine in inhibiting myopia.

Orthokeratology in controlling myopia of children: a meta-analysis of randomized controlled trials

BACKGROUND

Delaying the development and lowering the progression of myopia in children is the focus of current ophthalmology researches. We aimed to evaluate the role of orthokeratology in controlling myopia of children, to provide insights to the clinical treatment and care of children with myopia.

METHODS

Two investigators searched the The Cochrane Library, Embase, Pubmed, China national knowledge infrastructure, China biomedical literature database, WanFang and Weipu databases for randomized controlled trials(RCTs) on the role of orthokeratology in controlling myopia of children up to November 5, 2022. Two researchers independently searched, screened and extracted the studies according to the inclusion and exclusion standards. RevMan5.3 software was used for statistical analysis.

RESULTS

A total of 14 RCTs involving 2058 children were included in this meta-analysis. Synthesized outcomes indicated that orthokeratology improved the uncorrected visual acuity(MD = 0.40, 95%CI: 0.05 ~ 0.74), reduced the diopter change(MD=-3.19, 95%CI: -4.42~-1.95), changes of corneal curvature(MD=-3.21, 95%CI: -3.64~-2.79), the length of ocular axis (MD=-0.66, 95%CI: -1.27~-0.06) and amount of ocular axis change(MD=-0.42, 95%CI: -0.64~-0.21) after 1 year of wearing orthokeratology(all P < 0.05). Besides, orthokeratology reduced the diopter change (MD=-3.22, 95%CI: -4.86~-1.58), the length of ocular axis (MD=-1.15, 95%CI: -2.25~-0.06) and the amount of ocular axis change after 2 year of wearing orthokeratology (MD=-0.53, 95%CI: -0.96~-0.11) after 2 year of wearing orthokeratology (all P < 0.05). No publication biases were found amongst the synthesized outcomes (all P > 0.05).

CONCLUSIONS

Orthokeratology delays the progression of myopia in children, the long-term effects of orthokeratology need further investigations in future studies.